1. Field
Anaerobic adhesive and sealant compositions in film form, film spool assemblies containing such compositions in film form and preapplied versions thereof on matable parts are provided.
2. Brief Description of Related Technology
The use of liquid polymerizable or curable substances for the purpose of sealing and locking interfitting parts is well known in the art. Early threadlocking compositions were applied in liquid form shortly before or at the time of assembly of the interfitting parts. The compositions were applied wet and cured only after the interlocking of the mated parts.
In many applications, wicking of the liquid composition into tight spaces between adjoining parts is desirable. However, in many situations the ability of the liquid adhesive to migrate from parts is problematic, causing contamination of sensitive parts. Moreover, in many maintenance applications, the spillage of liquid adhesive compositions can be deleterious as well as inconvenient.
U.K. Patent Application No. GB 2060669 (Moran) speaks to anaerobically curing rubber adhesive compositions, which may be in the form of sheets, tapes, ribbons or latex. Moran uses a rubber in an amount of 30% to 80% by weight in the composition, presumably to assist in processing the composition to form the film. However, the large amount of rubber reduces the ability to form a robust bond when assembled between two matable parts.
One attempt to create a convenient ready-to-use threadlocking product has been the use of preapplied adhesive compositions, such as those in latex or micro-encapsulated form.
In such cases, the adhesive composition is applied to the threaded part, such as a bolt or nut, and remains in the uncured state until mated. As an example of a known preapplied adhesive composition, U.S. Pat. No. 4,497,916 discloses a continuous liquid phase adhesive composition to which is added solid wax-like particles dispersed therein. These particles may be chosen from polyethylene glycol materials having 4,000 to 20,000 molecular weight, stearic acid, acid waxes or stearic esters. The compositions disclosed in the '916 patent are formed by heating this combination of materials in slurry form and applying it, while heated, to threads. The composition then cools to obtain a non-mobile coating. This composition requires substantial preparation in order to obtain the composition and apply it on parts.
Such locking compositions, however, were not suitable for many applications in industries with high rates of assembly and mass production, such as the automotive industry.
As a result pre-applied sealant and locking coatings were developed for use in these industries. Indeed, pre-applied sealant coatings are now preferred in such industries due to their many advantages. Pre-applied sealant or locking coatings which were initially developed were deposited on threaded fasteners as dry to the touch coatings in which uncured polymerizable fluids were encapsulated or skinned over within a dry coating on the fastener. Assembly of the fasteners with a corresponding threaded part, e.g. a nut, caused fracture of the microcapsule coating or skin and exposure of the underlying polymerizable fluid to curing conditions, e.g. anaerobic cure.
For instance, U.S. Pat. No. 4,325,985 describes a method in which a polymerizable fluid material is deposited on a threaded part, and a separate fluid film-forming cover coat is applied thereover immediately after, forming a thin, solid, dry, non-tacky film by brief exposure to radiation, such as ultra-violet radiation. The radiation-curable film-forming cover coat is cured through its depth, leaving the polymerizable locking material still fluid for subsequent cure upon mating of threaded parts. The radiation-curable film is a protective skin designed to be dry and non-tacky.
U.S. Pat. No. 4,632,944 discloses a dual curing composition for use on threadlocking articles. The first curing mechanism is initiated by radiation such as ultraviolet radiation light. An opacifier, such as a powder, is dispersed therein rendering the polymerizable solution opaque to the radiation beyond the surface layer. A dry tack free crust is therefore formed on the surface. The second polymerization mechanism is thereafter initiated on the remaining polymerizable fluid once the two engineering parts are assembled together.
Pre-applied fasteners, i.e. fasteners having a sealant or locking composition on their threads, are normally shipped in bulk. They are often loose in the shipping container and in direct contact with each other. Pre-applied fasteners which rely on a protective skin over a fluid sublayer have a potential for rupture of the skin in the shipping containers or storage, with subsequent leakage of the polymerizable composition is common, resulting in unusable parts. Fasteners may adhere to each other due to this leakage, or be difficult to handle due to uncured liquid contaminating their exterior. In such cases, the fastener product is rendered unusable. Further, the skin enclosing the polymerizable fluid is usually not an integral part of the final polymerized composition. The adhesive force of the resultant bond may not be as great as if it were the polymerizable fluid alone.
Other alternatives to the skinned over uncured liquid versions of pre-applied threadlocking products have been developed. Fully cured latex coatings are a known alternative for sealing purposes. Cured latex coatings do not suffer from potential rupture of polymerizable liquid, but are expensive to produce because they require oven curing at relatively high temperatures for 45 minutes or longer. The most common method used in the industry today to dry latex coatings is to employ the use of a gas fired oven. Typically the forced hot air is recirculated within the confines of the oven's inner housing. Temperatures are typically maintained at 155° F. (68° C.) or so). This method of drying is costly and its relative inefficiency is increased by heat loss at the entrance and exit of the conveyor belt openings which run through the housings of conventional industrial ovens. Care must also be exercised so that the temperature does not reach the point of creating steam which causes creators on the surface of the coating. When creators are present, the integrity of the adhesion is compromised and the coating will chip and peel off the threaded fastener, as well as creating an undesirable appearance. It becomes necessary to control the ramp-up speed and allow the fastener to uniformly heat through to avoid removing the water too rapidly. Moreover, latex coatings often become brittle and flake or peal during storage, particularly if exposed to uncontrolled environmental conditions. Additionally, dried latex coatings do not possess the capability to be further physically tailored or altered to the particular needs of threaded applications.
Henkel Corporation recently introduced a line of products based on anaerobically curable compositions in non-flowable form. These products—or anaerobic sticks, as they are frequently called—are prepared from at least one room-temperature flowable polymerizable compound; and a polymeric matrix selected from urea-urethanes, hydroxy or amine-modified aliphatic hydrocarbons, polyester-amide-based rheological additives and combinations thereof. The polymeric matrix is present in an amount sufficient to render the composition non-flowable at temperatures up to about 180° F. (82° C.) and dispensable at room temperature without application of heat.
While tremendously successful, the anaerobic stick product line does not address the desire of many end users to have an anaerobic adhesive or sealant film product or an anaerobic adhesive or sealant preapplied product.